<template>
  <div class="pagination">
    <button @click="$emit('currentPage',pageNo -1)" :disabled="pageNo == 1">上一页</button>
    <button v-if="startAndEnd.start > 1">1</button>
    <button v-if="startAndEnd.start > 2">···</button>

<!-- 中间连续页码的地方：用v-for遍历出来 -->
    <button v-for="page in startAndEnd.end" :key="page" v-if="page >= startAndEnd.start" @click="$emit('currentPage',page)" :class="{active:pageNo == page}">{{page}}</button>

    <button v-if="startAndEnd.end < totalPage -1">···</button>
    <button v-if="startAndEnd.end < totalPage" @click="$emit('currentPage',totalPage)">{{totalPage}}</button>
    <button  @click="$emit('currentPage',pageNo + 1)" :disabled="pageNo == totalPage">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["total", "pageSize", "pageNo", "pagerCount"],
  computed: {
    // 分页器一共有多少页【总条数/每页展示的条数】
    totalPage() {
      // 有小数的话 向上取整 Math.ceil
      return Math.ceil(this.total / this.pageSize);
    },
    // 接着计算出连续五个数字，开头 ，结尾
    startAndEnd() {
      // 算出连续页码数：开始与结束这两个位置
      let start = 0,
        end = 0;
        // 解构赋值共有多少页。中间连续的数字，当前所在的页数
        const {totalPage,pagerCount,pageNo} = this;

        // 特殊情况：总页数小于连续页码数
        if(totalPage < pagerCount){
            start = 1;
            end = totalPage;

        }else{
            // 正常情况：分页器总页数大于连续页码数
            start = pageNo - parseInt(pagerCount / 2);
            end = pageNo + parseInt(pagerCount /2);

            // 要约束start 与 end 在合理的范围内
            // 约束头部
            if(start < 1){
                start = 1;
                end = pagerCount;
            }

            // 约束尾部
            if(end > totalPage){
                end = totalPage;
                start = totalPage - pagerCount + 1;
            }
        }

        // 返回开始 与 结束的值
        return {start,end}
    },
  },
};
</script>

<style lang="less" scoped>
.pagination {
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>